Hitherto, the CDMA method has been put into a practical use as the efficient wireless transmission. In the CDMA method, transmitting data is diffused using an orthogonal code and is multiplexed to be transmitted. There is a case in which control information (power control information, information for synchronous detection and the like) other than user information (audio data or packet data or the like) is contained in the transmitting data.
FIG. 11 is a block diagram showing a conventional example in which wireless transmission processing is performed in the CDMA method by multiplexing user information and control information. First, the user information is supplied to a mapping circuit 71 to perform mapping processing in which data 0 is set to 1 and data 1 is set to −1, and the mapped user information is supplied to a diffusion circuit 72 and is multiplied by an orthogonal code c1 to be diffused. The diffused user information is supplied to a power amplifier 73 to perform amplification processing according to transmission power and is supplied to a composing unit 74.
On the other hand, the control information is also supplied to a mapping circuit 75 to perform mapping processing in which data 0 is set to 1 and data 1 is set to −1, and the mapped control information is supplied to a diffusion circuit 76 and is multiplied by an orthogonal code c2 to be diffused. The diffused control information is supplied to a power amplifier 77 to perform amplification processing according to transmission power, and an amplified signal is supplied to the composing unit 74 after made into a complex number in a complexing circuit 78.
In the composing unit 74, the supplied user information and control information as information of I channel and that of Q channel respectively are made into one system of information (I+jQ), in which the above user information and control information are orthogonally composed, and the information (I+jQ) output from the composing unit 74 is supplied to a scramble circuit 79. In the scramble circuit 79, a complex multiplication is performed using a scrambling code to be made into a scrambled signal, and the scrambled signal is transmitted.
When it is tried to raise a transmission rate in such CDMA method, a method of multiplexing transmitting data using, for example, a plurality of orthogonal codes has been known. FIG. 12 is a diagram showing an example of a configuration on a transmitting side to which conventional multi-code processing for multiplexing the transmitting data using a plurality of orthogonal codes is applied, and FIG. 13 is a diagram showing an example of a configuration on a reception side for the signal thereof. Processing of mapping, power control and the like is omitted in FIGS. 12 and 13.
An explanation is made to the configuration of FIG. 12; transmitting data is divided into a plurality of data series in a serial/parallel converter 81. Hereupon, it is assumed that the data is divided into n (n is an arbitrary integer and the number of multiplexing) series; and the n series of data are supplied to different diffusion circuits 82a, 82b, - - - and 82n respectively and are multiplied by different orthogonal codes c1, c2, - - - and cN respectively to perform diffusion processing multiplying. The transmitting data which are diffused by the respective diffusion circuits 82a, 82b - - - and 82n are provided for different modulation circuits 83a, 83b, - - - and 83n respectively to perform modulation processing for transmission, and the modulated transmitting data are supplied to a multiplexing circuit 84 to be made into multiplexed transmitting data and the transmitting data is wirelessly transmitted.
FIG. 13 is a diagram showing an example of a configuration of receiving a signal which is thus multiplexed and wirelessly transmitted. Received data is supplied to a plurality of inverse diffusion circuits 91a, 91b, - - - and 91n. Those inverse diffusion circuits 91a through 91n are n pieces of circuits which are prepared to correspond to the multiplexing number of n at the time of transmission, and data are multiplied by the same diffusion codes c1, c2, - - - and cN as those at the time of transmission in the respective inverse diffusion circuits 91a, 91b, - - - and 91n to perform inverse diffusion processing on the data series which are diffused using the respective diffusion codes. The receiving data obtained from the inverse diffusion processing for each series of data are supplied to different demodulation circuits 92a, 92b, - - - and 92n respectively to perform demodulation processing for receiving data, and each series of the demodulated receiving data is composed into one data series in a parallel/serial conversion circuit 93 to be made into the receiving data.
With performing the transmission processing of the multiplexed signal using the plurality of orthogonal codes shown in those FIGS. 12 and 13, it is possible to increase an amount of data to be transmitted as the number of diffusion codes to be used increases, and the transmission rate can be raised to that extent. The following reference discloses an example of specification in which transmission is performed after multiplexing by the plurality of orthogonal codes.
“3G TS 25.211”, issued by 3GPP (Dec., 1999), V3.1.1 Technical Specification 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Physical channels and mapping of transport channels onto physical channels, the 20th page.
However, when wireless transmission is performed in the manner shown in FIGS. 12 and 13, there is a problem in which transmitting power is required as much as the number of orthogonal codes to be used. In other words, when two orthogonal codes are used, twice as much transmitting power is required, and when four orthogonal codes are used, the transmitting power four times as much is required, and therefore, there has been a problem in which a great amount of transmitting power is necessary as a whole in proportion to the number of orthogonal codes to be used.
In order to avoid this problem, there is a method of, for example, raising a transmission rate by shortening a cycle of an orthogonal code. However, when the cycle of the orthogonal code is shortened, noise characteristics become deteriorated to that extent, and therefore, it becomes necessary to increase the transmitting power, after all.
Further, although it is also considered to raise the transmission rate by employing a modulation method of using multiple values, the noise characteristics also deteriorate in this case and therefore, the transmitting power needs to increase after all. When a QPSK (Quadrature Phase Shift Keying) method, for example, has been employed as the modulation method, it can also be considered to switch over to a multi-value modulation such as a 16QAM (Quadrature Amplitude Modulation) method. However, since a distance between signals becomes short when switching over to the multi-value modulation, the noise characteristics become deteriorated and the transmitting power needs to increase in order to secure a communication quality.
Particularly, in case of a communication terminal such as a mobile phone unit which is operated using a battery, such large increase in transmission power is not desirable due to the reason that sustaining time of the battery of the terminal may be shortened.
The present invention is made in view of the above problems and aims to raise the transmission rate efficiently without increasing the transmission power.